Concrete undergoes a curing process after it is poured. Immediately after pouring, the concrete is in a plastic state. From this state, the poured concrete begins to transform from a fluid state to a solid state, becoming more dense and rigid. As this occurs, the concrete begins to “bleed,” i.e. solid particles in the concrete begin to settle and water in the concrete begins to migrate upward to the surface.
Concrete must have enough time under the proper conditions to cure to the desired strength. Properly cured concrete is more resistant to stress, abrasion and mechanical issues resulting from repeated freezing and thawing. Properly cured concrete is also more resistant to scaling, creep and failure. Problems with concrete frequently start at the surface. Properly curing the top 3 inches of a concrete member and, in particular, the top 3/16 of an inch, can prevent many of these problems.
Proper hydration of curing concrete contributes to proper curing. One known method for hydrating curing concrete is to spray it with water and cover it with a curing blanket. Generally speaking, curing blankets are used to maintain moisture in poured concrete during the curing process. Examples of such products are discussed in U.S. Pat. Nos. 1,694,588, 8,852,380, 7,572,525, 7,998,564, 5,780,367 and 5,611,369.
The present invention includes multiple methods and apparatuses for curing concrete. These methods and apparatuses include, but are not limited to, (1) curing covers for poured concrete members, (2) curing covers for use during the storage, transportation and after installation of concrete structures, (3) methods of making curing covers, (4) methods of altering the pH of the water used to hydrate curing concrete members, and (5) barrier layers for poured concrete.
In one embodiment of the present invention, an apparatus for curing concrete includes a film having a first outer layer, a second outer layer, a first inner layer, a second inner layer, a third inner layer, a fourth inner layer and an absorbent layer. The first and second outer layers include linear low density polyethylene. The first inner layer is adjacent the first outer layer and the second inner layer is adjacent the second outer layer. The first and second inner layers include linear low density polyethylene and high density polyethylene. The third inner layer is adjacent the first inner layer and the fourth inner layer is adjacent the second inner layer and the third inner layer. The third and fourth inner layers include an ethylene polypropylene copolymer. The absorbent layer includes a nonwoven fabric. An adhesive material adheres the second outer layer of the film to the absorbent layer.
In one embodiment, the first outer layer of the film includes an antiskid component. In one embodiment, the kinetic and static coefficients of friction of the first outer layer of the film are each at least 0.7.
In another embodiment, the nonwoven fabric includes a plurality of raised areas and a plurality of recessed areas and the adhesive adheres the second outer layer of the film to the raised areas of the nonwoven fabric.
According to another embodiment, the apparatus further includes a pH modifying component for modifying the pH of water used to hydrate the curing concrete. The pH modifying component may be incorporated into the film and/or the absorbent layer. In certain embodiments, the pH modifying component includes calcium oxide. The pH of water used to hydrate the curing concrete may be about 11 to about 13.
In another embodiment, the film forms a water vapor barrier on one side of the absorbent layer. In certain embodiments, the water vapor transmission rate of the apparatus from the absorbent layer through the second inner layer of the film is less than 10 grams per square meter per day.
In other embodiments, the apparatus has a puncture resistance of at least 14 pounds. In some embodiments, the apparatus has an Elmendorf tear strength of at least 1,000 grams. In certain embodiments, the first and second outer layers of the film include ethylene butyl acrylate.
In another embodiment of the present invention, a method of manufacturing an apparatus for curing concrete includes providing a film, providing an absorbent material, the absorbent material having a plurality of raised surfaces and a plurality of recessed areas, providing an adhesive material, heating the film to its crystalline softening point, applying the adhesive material to the raised surfaces of the absorbent material, and adhering the film to the raised surfaces of the absorbent material so as to form a plurality of pockets bounded by the recessed areas of the absorbent material and the film.
In one embodiment of the invention, the absorbent material and adhesive material are laminated together. In another embodiment, the adhesive material is a hot melt adhesive. In certain embodiments, the resulting apparatus has a saturated bond strength of at least about 22 grams per inch.
In another embodiment of the present invention, a method of curing of concrete includes pouring concrete to a desired shape to form a concrete member, waiting for the concrete to reach the bleed stage, applying hydration water to the surface of the poured concrete, and applying an apparatus over the surface of the concrete after applying the hydration water, the apparatus including a film, an absorbent layer adhered to the film and a pH modifying component for modifying the pH of the hydration water.
In one embodiment, the apparatus further includes a pH modifying component for modifying the pH of water used to hydrate the curing concrete. The pH modifying component may be incorporated into the film and/or the absorbent layer. In certain embodiments, the pH modifying component includes calcium oxide. The pH of water used to hydrate the curing concrete may be about 11 to about 13. In one embodiment, the method includes maintaining the pH of the hydration water above about 11 for at least 7 days.
In another embodiment, the film forms a water vapor barrier on one side of the absorbent layer. In some embodiments, the water vapor transmission rate of the apparatus from the absorbent layer through the film is less than 10 grams per square meter per day.
According to another embodiment of the invention, the film includes an antiskid component. In certain embodiments, the apparatus is configured to enclose the concrete member.
In yet another embodiment of the invention, the step of applying the apparatus to the concrete member includes enclosing the concrete member in the apparatus and transporting the enclosed concrete member to a location other than the location at which it was poured, thereby continuing to cure the concrete member during transport.
In another embodiment of the present invention, an apparatus for providing a barrier layer between the ground and concrete to be poured on the ground includes a film having a first outer layer, a second outer layer, a first inner layer, a second inner layer, a third inner layer and a fourth inner layer. The first and second outer layers include linear low density polyethylene. The first inner layer is adjacent the first outer layer and the second inner layer is adjacent the second outer layer. The first and second inner layers include linear low density polyethylene and high density polyethylene. The third inner layer is adjacent the first inner layer and the fourth inner layer is adjacent the second inner layer and the third inner layer. The third and fourth inner layers include an ethylene polypropylene copolymer.
These and other features of the present invention will be apparent to one of ordinary skill in the art from the following description and accompanying drawings.